1. Field of the Invention
The present invention relates to the sorting, storage and retrieval of objects, and in particular, to the sorting of objects from a single source stream into a plurality of destination streams, and the storage and retrieval of objects between a single storage and retrieval stream and a plurality of storage locations.
2. Statement of Related Art
In the field of package shipping, packages are received from many areas of the country, or even the world, for distribution to a variety of other areas. Packages arrive at distribution centers in groups sharing common sources and leave in groups sharing common destinations. Thus, shipments of common-source packages must be efficiently sorted into shipments of common-destination packages.
Affixed to each package is a shipping label containing, along with other information, the zip code of the package destination. The zip codes of the possible package destinations are organized into twelve different categories, with each zip code falling in only one category.
In many known sorting systems, a shipment of packages arrives at a distribution center, usually by truck. The packages are unloaded from the truck onto a feed conveyor which transports the packages to a worker who sorts them. In prior art sorting systems, this sorter reads the zip code of the destination address of each package as it arrives at the end of the feed conveyor. The sorter determines the appropriate zip code category corresponding to the zip code of each package.
Adjacent to the sorter is an array of twelve receiving conveyors, arranged in three different levels of four receiving conveyors each. Each receiving conveyor corresponds to one of the twelve zip code categories. The sorter must pick up the package from the end of the feed conveyor, turn toward the array of receiving conveyors, and place the package onto the correct receiving conveyor.
Each package is then advanced along its appropriate receiving conveyor. A package may then be loaded for further shipment or may continue through one or more similar sorting operations before being loaded for further shipment. A distribution center may also have multiple shipment acceptance points. As a result, as many as 20 or 60 sorters may be operating simultaneously in a distribution center.
There are many problems with these prior art systems. For example, complicated training of employees must be provided to enable them to perform the sorting operations. Furthermore, different sorting stations may have different categories of zip codes. Therefore a sorter must know the system of categorization of zip codes for an individual sorting station. As a result, a sorter must be familiar with virtually all the addresses in the country in order to be able to operate at different sorting stations.
To operate effectively, a sorter must be able to recognize and select the correct receiving conveyor with about 99.9 percent effectiveness. This limits the pool of potential laborers who are able to qualify as sorters. Additionally, the package shipping business is growing faster than the supply of potential laborers who can perform the physically and mentally demanding tasks of the sorter.
Furthermore, very difficult physical demands are imposed upon a sorter. A typical sorter may sort approximately 1000 packages an hour over an approximately three and a half hour shift. A typical sorter's physical capabilities limit package weight to about 70 pounds and package size to about 5 feet in any dimension. The number and arrangement of receiving conveyors is also limited by the physical size of the sorters. A typical sorter is only able to place packages safely and securely on receiving conveyors that are no more than about five feet above ground level.
The timing of the work shifts of the sorters throughout the day further reduces the size of the available labor pool. Sorting activity consists of four shifts distributed roughly evenly through the day and night. Thus, the three-and-a-half hour shifts are separated by roughly two and a half hours, during which sorting activity is not required.
Furthermore, sorters make errors. They may place packages on the wrong receiving conveyors. They may drop or otherwise damage packages. Additionally, they are subject to injury when sorting packages.
The prior art teaches automatic sorters that are adapted to sort objects. U.S. Pat. No. 4,867,299, issued to Fukuoka et al. on Sep. 19, 1989, teaches a distributor for distributing veneer sheets wherein a single source stream of veneer sheets is divided into two vertically arranged destination streams of veneer sheets. This distributor solves some of the physical limitations inherent in the use of humans in known package sorting systems. For example, the distributor of Fukuoka et al. can work continuously for longer periods of time than a human. Furthermore, it is able to distribute larger and heavier packages than a single human can handle safely. In addition, such an apparatus has the advantage of being able to receive one package from the feed conveyor at the same time that it is depositing another package onto one of the receiving conveyors.
However, the distributor taught by Fukuoka et al. does not solve all the problems associated with known package sorting systems. Foremost is that distribution by such a distributor is not sorting. For example, package sorting involves the selective distribution of packages according to their zip codes. The distribution performed by the distributor taught by Fukuoka et al. is simple alternation between the upper and lower destination streams. This distributor distributes every other object to the upper destination stream and the rest of the objects to the lower destination stream, without any regard to differences between the objects distributed. Such a distributor cannot sort packages according to their desired destinations in the field of package shipping.
Another problem with the distributor taught by Fukuoka et al. is that it is limited to two destination streams. Known package sorting systems require a sorter to be able to sort a single source stream of packages into at least twelve destination streams. Although the distributor taught by Fukuoka et al. could distribute to twelve destination streams, stacking twelve receiving conveyors would require an excessive amount of vertical space and an excessive amount of travel to place the objects on a selected receiving conveyor. Furthermore, the distributor taught by Fukuoka et al. could not distribute packages to the twelve receiving conveyors in known package sorting systems, since those receiving conveyors are arranged in arrays of rows and columns of receiving conveyors.
U.S. Pat. No. 4,326,624, issued to Ewertowski et al. on Apr. 27, 1982, teaches a pallet changer which may be applied to known package sorting systems. The pallet changer taught by Ewertowski et al. sorts pallets from a single source stream of pallets into a plurality of destination locations arranged in a circle about the pallet changer. The pallet changer distributes one pallet at a time from the single source stream to a selected destination. The destination is selected according to characteristics of the particular pallet being sorted.
However, the pallet changer taught by Ewertowski et al. does not solve all the problems associated with known package sorting systems. A sorting system such as the pallet changer taught by Ewertowski et al. that contained twelve receiving conveyors arranged in a circle about the pallet changer would require an excessive amount of horizontal space. Furthermore, the distributor taught by Ewertowski et al. could not distribute packages to the known package sorting systems having twelve receiving conveyors arranged in arrays of rows and columns.
Thus, the prior art does not teach a mechanical sorter capable of solving the problems of known package sorting systems which require distribution to an array of receiving conveyors.